need to test K250-1 [message #28376] |
Fri, 05 November 2021 04:42 ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
coatikid
Messages: 4 Registered: November 2021
|
Junior Member |
|
|
I picked up a K250-1 on auction and brought it home. It's bare metal, no tuck and roll, etc. Are there kits or replacements? The plastic sleeve on the power switch had broken off. Thanks to the community member who suggested on someone else's post that you can use zip ties to secure the switch to the mounting bracket. Works! My question is, without a suitable cab to test out this unit, how can I test this K250-1? Thanks
|
|
|
Re: need to test K250-1 [message #28377 is a reply to message #28376] |
Fri, 05 November 2021 06:09 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
stevem
Messages: 4764 Registered: June 2004 Location: NY
|
Senior Member |
|
|
Hello and welcome!
First off since you fixed the switch ( that's my cable tie repair tip by the way ) have you had the amp powered on which will be indicated by one or both of the lights in the two front switches coming on.
You do not need the amp plugged into a speaker to power it up, but You can test the amp into any 4,8 or 16 ohm speaker if you have one.
I good thing to do though when you turn it on for the first time would be to hook up a volt meter to the end of a speaker cable plugged into the amp.
The meter should be set for D.C. Volts.
On power the meter will read well over 1 volt if the output stage of the amp is bad, and this will be a constant DC volt reading.
If you do not have a voltmeter to do this check then you can just plug a speaker in to see if the amp is ok, but if it does have a output stage problem then you will get a loud hum out of the speaker.
This D.C. Voltage can blow a speaker if it's not rated for 75 watts or more.
Perhaps the best thing to do is to first check if the fuse is blown mounted on the rear wall of the amp.
If it is then the output stage has at least one blown output Transistor and one blown driver Transistor.
Please report back on how things go.
Ps. These amps want a 4 ohm load to outout there full amount of wattage that they can.
A 8 ohm load will provide about 75 watts of clean power output and a 16 ohm load will be half of that.
[Updated on: Fri, 05 November 2021 06:13] Report message to a moderator
|
|
|
|
|
|
Re: need to test K250-1 [message #28390 is a reply to message #28376] |
Sat, 20 November 2021 06:15 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
stevem
Messages: 4764 Registered: June 2004 Location: NY
|
Senior Member |
|
|
Ok, the first thing your going to need is to get a hand held tube type solder sucker since your going to need such to get some Transistors and maybe resistors off of the output driver board ( PC 5065 ) on the floor of the amp.
Since you have a meter, set it to ohms .
On the driver board you will see 4 big 5 watt box type ciramic resistors next to each of the 4 output driver Transistors in there heat sinks.
These are very low ohms and should not check open, and many times when the output section has a problem like your amp one or more of these resistors ( called emitter resistors) will over heat and go open.
On the schematic you found in your amp these four are resistors r 23, r25, r33 and r35.
Please report back on your findings and we will move on.
[Updated on: Sat, 20 November 2021 06:17] Report message to a moderator
|
|
|
|
|
|
Re: need to test K250-1 [message #28394 is a reply to message #28376] |
Wed, 24 November 2021 12:31 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) |
stevem
Messages: 4764 Registered: June 2004 Location: NY
|
Senior Member |
|
|
While you are waiting on the sucker you should go on line and learn how to test out transistors with your voltmeter .
|
|
|